Spec Conformance Review: SDK Span creation

[MrAlias]

• Review SDK Span creation section of the specification and identify all normative requirements it contains.
• Validate our implementation of the specification to conform or not. If it conforms, document the conformity here. If it does not open an Issue or PR track the work.
• Review the Traces/New Span ID created also for non-recording Spans section of the Spec Compliance Matrix.
• Update the matrix with the current state of Go (existing entries for Go should be ignored). If Go does not provide support for an item listed be sure to link to the Issue/PR tracking the work to support it.

[MrAlias]

SDK Span creation

When asked to create a Span, the SDK MUST act as if doing the following in order:

1. If there is a valid parent trace ID, use it. Otherwise generate a new trace ID
   (note: this must be done before calling ShouldSample, because it expects
   a valid trace ID as input).

opentelemetry-go/sdk/trace/span.go

Lines 529 to 536 in 8b1be11

	if hasEmptySpanContext(parent) {
	// Generate both TraceID and SpanID
	tid, sid = cfg.IDGenerator.NewIDs(ctx)
	} else {
	// TraceID already exists, just generate a SpanID
	tid = parent.TraceID()
	sid = cfg.IDGenerator.NewSpanID(ctx, tid)
	}

2. Query the Sampler's ShouldSample method
   (Note that the built-in ParentBasedSampler can be used to
   use the sampling decision of the parent,
   translating a set SampledFlag to RECORD and an unset one to DROP).

opentelemetry-go/sdk/trace/span.go

Line 561 in 8b1be11

samplingResult := makeSamplingDecision(data)

3. Generate a new span ID for the Span, independently of the sampling decision.
   This is done so other components (such as logs or exception handling) can rely on
   a unique span ID, even if the Span is a non-recording instance.

A new span ID is generated here:

opentelemetry-go/sdk/trace/span.go

Lines 526 to 543 in 8b1be11

	var tid trace.TraceID
	var sid trace.SpanID
	if hasEmptySpanContext(parent) {
	// Generate both TraceID and SpanID
	tid, sid = cfg.IDGenerator.NewIDs(ctx)
	} else {
	// TraceID already exists, just generate a SpanID
	tid = parent.TraceID()
	sid = cfg.IDGenerator.NewSpanID(ctx, tid)
	}
	span.spanContext = trace.NewSpanContext(trace.SpanContextConfig{
	TraceID: tid,
	SpanID: sid,
	TraceFlags: parent.TraceFlags(),
	TraceState: parent.TraceState(),
	})

it is done prior step 2, but step 2 has no influence on the Span ID value:

opentelemetry-go/sdk/trace/span.go

Lines 608 to 619 in 8b1be11

	func makeSamplingDecision(data samplingData) SamplingResult {
	sampler := data.cfg.DefaultSampler
	return sampler.ShouldSample(SamplingParameters{
	ParentContext: data.parent,
	TraceID: data.span.spanContext.TraceID(),
	Name: data.name,
	HasRemoteParent: data.remoteParent,
	Kind: data.kind,
	Attributes: data.attributes,
	Links: data.links,
	})
	}

In this sense it is "act[ing] as if doing" the step in order.

4. Create a span depending on the decision returned by ShouldSample:
   see description of ShouldSample's return value below
   for how to set IsRecording and Sampled on the Span,
   and the table above on whether
   to pass the Span to SpanProcessors.
   A non-recording span MAY be implemented using the same mechanism as when a
   Span is created without an SDK installed or as described in
   wrapping a SpanContext in a Span.

opentelemetry-go/sdk/trace/span.go

Lines 562 to 587 in 8b1be11

	if isSampled(samplingResult) {
	span.spanContext = span.spanContext.WithTraceFlags(span.spanContext.TraceFlags() | trace.FlagsSampled)
	} else {
	span.spanContext = span.spanContext.WithTraceFlags(span.spanContext.TraceFlags() &^ trace.FlagsSampled)
	}
	span.spanContext = span.spanContext.WithTraceState(samplingResult.Tracestate)
	if !isRecording(samplingResult) {
	return span
	}
	startTime := o.Timestamp
	if startTime.IsZero() {
	startTime = time.Now()
	}
	span.startTime = startTime
	span.spanKind = trace.ValidateSpanKind(o.SpanKind)
	span.name = name
	span.hasRemoteParent = remoteParent
	span.resource = cfg.Resource
	span.instrumentationLibrary = tr.instrumentationLibrary
	span.SetAttributes(samplingResult.Attributes...)
	span.parent = parent

[MrAlias]

spec-compliance-matrix

Feature	Go
New Span ID created also for non-recording Spans	+

New Span IDs are created for all spans.